Friday 8 April 2005 19.06 EDT
First published on Friday 8 April 2005 19.06 EDT

A conversation with Dr Helen Fisher has strange after-effects. While talking to my husband, I am suddenly anxious we have not done anything "novel" — one of Fisher's favourite words — for some time. Perhaps the dopamine levels in my brain are falling. Maybe the romance will disappear from our relationship. Awareness of the chemical comings and goings that underpin one's marriage is unsettling, to say the least.

But I don't think Fisher is unsettled. For 20 years, the anthropologist and autodidactic neuroscientist has relentlessly focused her curiosity on love, in all its shapes and forms, an interest that led her to write a book on the subject, Why We Love: The Nature And Chemistry Of Romantic Love (Owl Books). "I believe that there are three distinctly different brain systems for mating and reproduction," she says — sex drive, romantic love and, third, attachment. "We know quite a lot about sex drive, which is associated with very high levels of testosterone, and there are plenty of scientists looking into oxytocin and vasopressin, two of the neurotransmitters [the chemicals that send signals around our mind] behind attachment, but I wanted to know what was behind romantic love."

She started with George Bernard Shaw, who once said that "love consists of overestimating the difference between one woman and another". Fisher realised that "this focus, the sense of uniqueness, of novelty", were "all symptoms of elevated levels of dopamine". She runs through other classic symptoms of romantic love (focused attention, mood swings, high levels of energy, separation anxiety), all similarly triggered by dopamine. Romantic love, she concludes, is a drive rather than an emotion. It is not the result of falling in love, but a chemical kick to set you moving towards reproduction.

To investigate her hypothesis, Fisher put 17 volunteers, all newly in love, into a functional magnetic resonance imaging machine to scan their brains, and then showed them photographs of their loved ones. The results showed exactly what she had hoped: the areas of the brain that produce and receive dopamine were lit up like Las Vegas. "It was a defining moment in my life."

For years, dopamine was said to be the "reward" chemical, but Fisher is convinced it's "part of the basic mating drive. It enables us to focus our energies on one person, thereby conserving courtship time." So dopamine may be the stick, not the carrot.

As we learn more about these brain chemicals, will we one day be able to medicate for or against love? "We already do, to some extent," says Fisher. "Prozac brings serotonin levels back up, and that, in turn, depresses dopamine production" — so it's hardly likely to incite romantic love. You can medicate yourself, too: orgasms stimulate the production of oxytocin, which keeps you attached, and novelty will release more dopamine into your brain and give you that love rush.

"They recently took a gene associated with attachment out of the prairie vole, which forms deep attachments, and put it into the meadow vole, which does not. And, by God, the meadow vole began to form a pair bond with a mate!"

Somewhere out there, they are probably synthesising the stuff already. Coming soon to a marriage counsellor's office near you?